Several possibilities already exist for patterning knitted pile fabric. Usually, such fabrics are produced on machines with cylinder and sinker ring by feeding a ground thread to all needles raised to the knit position and thereafter retracted to the feeding position, the ground thread being fed under the nebs of the sinkers selected ones of which are then moved by a selection device (pattern wheel) so that their nebs come between the shafts of the needles. The pile threads are fed to the needles simultaneously above the sinker nebs and then the needles are retracted to the knock-over or cast-off position. In this way, pile loops are formed from the pile thread above all selected sinker nebs, while ground and pile threads are laid as short sinker loops over the knock-over edges of the unselected sinkers. Colour patterning is effected by feeding different coloured pile yarns at successive feeders and selecting each sinker usually only once during a colour cycle.
It is moreover already known from U.S. Pat. No. 2,710,527 to actuate all sinkers for pie loop formation, but either to raise the needles to the knit position or leave them in the miss position, by means of a patterning device. The unselected needles pick up neither ground nor pile threads. The fabric produced by this method is in any event known from DE-PS 664.750.
A further possibility for patterning pile fabric is given in U.S. Pat. No. 2,715,824. Here, a ground thread is fed to all fully raised needles and these are then retracted to an intermediate position in which selected needles are again raised to the tuck position and a pile thread is fed to them.
The combination of the selection of sinkers with the selection of needles is described in DE-PS 681.180. By combination of sinker and needle selection, it is possible to select sinkers to form pile loops between knitting needles in pile sections while sinkers are not selected between such pile sections, individual needles being raised to the tuck position in order to tuck in ground and pile threads so that these threads are alternately tucking and missing in these sections (laid-in threads).
The possibility of knitting two pile threads with one ground thread according to DE-PS 664.750 is known from the method described in DE-PS 671.333.
A number of possibilities for producing patterned pile fabrics would also apply to machines with cylinders and dials. The task of forming pile loops on the sinker nebs is then taken on by one of the two sets of needles (e.g. DE-PS 706.809) or the pile sinkers provided instead of one set of needles (e.g. DE-PS 1.221.756) or pile hooks (e.g. DE-PS 1.816.846, U.S. Pat. No. 3,241,337, DE-OS 2 704 295, DE-OS 2 918 903).
The methods referred to and the fabrics produced thereby have a number of disadvantages.
Colour patterns according to the current method, in which only selection of the pile elements is effected, have a reduced pile density dependent on the colour cycle. Thus, in a two colour pattern, pile loops will be formed in a plain coloured area only in every second course. Between these courses having pile loops run normal courses in which the other coloured pile thread is knitted and thereby partially strikes through. By using this thread thus when it is not used for pile loop formation, a substantial part of it is needlessly wasted.
Colour patterns according to U.S. Pat. No. 2,710,527 are characterised by high pile density. Since the ground threads of one pattern colour are floating over the pattern area knitted from the other ground threads, these floats limit the width of single colour pattern areas, since--in order to bring the pattern into evidence--the floated pile threads must be cropped and removed. In doing this, the longer ground thread floats could also be raised and cut, as a result of which the fabric will have faults.
Through the laying-in of the ground and pile threads in a desired pattern as described in DE-PS 681.180 it is certainly possible to have a large scale pattern, but, however, this has the disadvantage that two separate knitting elements in the knitting process--needles and sinkers--have to be selected synchronously with regard to each other. Thus not only is the machine expensive, but increased costs are also incurred for the setting up, adjusting and monitoring of the pattern. This also applies to the possibility described in BG-PS 813,357 to interrupt the pile formation. Here too the pile-forming elements and the needles producing the ground fabric must be separately controlled, but synchronised one with the other. This has the disadvantage that the pile threads are fed ahead of the ground threads. As the latch needles must be raised to the knit position between pile and ground threads, their hooks therefore rise over the pile elements and can, particularly at the edges, readily engage the pile threads unintentionally and knit them.
If one tries to produce colour patterning according to U.S. Pat. No. 2,715,824, one could save a substantial amount of pile material as compared with the previously described methods. After being fed, the ground thread is guided over the sinker nebs and only drawn under the sinker nebs during the feeding of the pile thread by means of unselected needles. In order to guarantee that the ground thread is guided under the sinker nebs, the unselected needles must be retracted, particularly when using low pile sinkers, very close to the knock-over edges of the sinkers. This does not prevent the risk that previously knitted stitches will slide over the needle head to form unintentional stitches whereby the unrestrained feeding of thread to the actual knitting operation is interrupted and this leads to faults in the knitting. It is however necessary that when selecting needles to take up the pile thread, not to select adjacent needles, otherwise the ground thread can rise with the needles and is not guaranteed to engage under the sinker nebs. The tendency of the ground thread to rise with the selected needles is increased because the closed latches of the rising needles have to be opened simply by thread tension, which presupposes a certain quality of material for the ground thread. As a result, the range of possible pattern specifications is limited; in any event, in colour patterning, a reduction of pile density must be accepted.
Patterned pile fabrics, in which, according to DE-PS 671.333, two pile threads are knitted alternately with a ground thread, exhibit the highest possible pile density, but the patterning is achieved by using seperate the sets of needles, which must be guided in separate cam-tracks independently of one another. While the two sets of needles engage the pile threads fed to them at the same height, one set of needles must be retracted after feeding the first pile thread, while the other is raised. This excludes the use of a conventional selection device which acts on only one set of butts and can thus only effect a movement of one set of needles. A further disadvantage is that while the first pile thread is fed between the minimally separated heads of the needles of the two sets it must nevertheless remain behind the lower needle heads of one set of needles. It will be appreciated by anyone skilled in the art that precise feeder adjustments and exact needle tolerances are required, since otherwise needles of the lower set that may be bent to the rear after the feeding of the first pile thread can lie in front of the pile thread on the next succeeding upstroke, or, alternatively, the pile thread feeder can be easily damaged by projecting or defective needles. Precise setting of the sinker ring is required in any event in order to lay the ground thread fed over the sinker nebs under, and the previously fed pie thread above the sinker nebs. From the drawings it can be clearly seen that the feeding of the ground thread under the sinker nebs is on that account not possible since for this the sinkers must be retracted further and then come too late for the first pile thread to be laid over the sinker nebs. According to this process, the number of pile threads that can be worked with in each complete machine course is limited to two.